TfL has finally revealed the problem that caused the delay in reopening a busy underground station.

Kentish Town Tube station has been closed since June 26 last year to replace old escalators, remove the "redundant" ticket office and realigning ticket barriers.

The work was due to be completed by early summer, but reopening was pushed back to September after TfL "identified assets that require essential repair".

Conservative mayoral candidate Susan Hall had written to the Labour mayor Sadiq Khan seeking answers about the  “absurd” delay.

After questions from this paper, TfL said that work demolishing the old ticket office has revealed unstable concrete - but this was not reinforced autoclaved aerated concrete (RAAC), and that asbestos was not found.

There has been frustration after the delay was announced. Shopkeepers said the prolonged closure was harming trade.

Police are also investigating after platform walls were plastered with graffiti.

In her letter, Ms Hall outlined concerns from residents and businesses, including those of women she had spoken to who have been forced to walk a longer distance home from Camden Town station in the dark. 

She said: “To close the station for more than a year in the first place, to replace two escalators and carry out basic maintenance work, seems mindbogglingly lengthy and to extend that further with such little detail or reassurance is unacceptable.

Ham & High: Bus stop closures due to bridge work in Kentish Town has added to the misery for locals that the closed tube station has causedBus stop closures due to bridge work in Kentish Town has added to the misery for locals that the closed tube station has caused (Image: Nathalie Raffray)

“With the further inconvenience of nearby Tube stations regularly having to close due to overcrowding, alongside the extended closure of local bus stops, the range of public transport options available for residents are seriously lacking, not least for women who are now having to walk much longer distances home in the dark after work."

A spokesperson for TfL said the concrete problem found during ticket office removal was "not a safety issue" but did mean work had to be carried out to secure it.

They added: "There are issues with the ceiling that couldn’t have been identified by surveys beforehand, so dealing with that has caused the delay."

Regarding any safety issues, the spokesperson said there is an "extensive" local bus network serving the area including the 134 from Archway and 88 and 214 from Highgate village and Parliament Hill, all running towards Camden Town Station. 

They also advise customers to use Kentish Town Thameslink station, or nearby Tufnell Park Tube station for Northern line services.

"We work extremely closely with our policing partners to help keep all those using the public transport network safe," they added.

The spokesperson said TfL will publicise the reopening date of the station as soon as it is in a position to do so.